JP5910482B2 - Optical fiber vibration sensor - Google Patents

Description

  The present invention relates to an optical fiber vibration sensor constituting a Sagnac interference system.

  In important facilities such as airports, harbors, power plants, public facilities and unmanned power plants where people gather, intrusion detection sensors are installed on fences installed around the site to detect suspicious intruders. Yes. Conventionally, an optical fiber vibration sensor using an optical fiber as the intrusion detection sensor has been proposed (see, for example, Patent Document 1).

  This optical fiber vibration sensor accommodates a light source, a light receiver, a first coupler (optical connection part), a polarizer, a second coupler (optical connection part), an optical fiber for connecting them, and a signal processing unit. A vibration sensor main body, an optical fiber loop connected to the vibration sensor main body to form a closed optical circuit, and two optical connectors connected to the vibration sensor main body and the optical fiber loop. A Sagnac interference system that detects the physical disturbance (vibration) applied to the optical fiber loop by transmitting the opposite optical signals to interfere with each other and circulating the optical signals and measuring the intensity change of the interference light. It is a sensor which constitutes.

JP 2006-208080 A

  However, in the conventional optical fiber vibration sensor, two optical connection parts are used to make the optical signal paths incompatible with each other. However, the output of the return optical signal transmitted to the light receiving element is the incident optical signal. On the other hand, since two optical connection portions are routed, the optical signal output is greatly attenuated by the branch loss of the optical connection portion before the output of the optical signal is transmitted to the light receiving element.

  Accordingly, an object of the present invention is to provide an optical fiber vibration sensor capable of reducing branch loss of an optical signal and capable of highly accurate vibration measurement by a reciprocal optical system.

[1] A light emitting element that outputs an introduction signal and outputs a detection optical signal that is amplified by a self-coupling effect by transmitting a return optical signal of the introduced introduction optical signal;
A light receiving element that receives the detection optical signal output from the light emitting element, converts the detection signal into an electrical signal, and outputs the electrical signal;
An optical connection for branching the introduction optical signal output from the light emitting element into a pair of optical signals and causing the pair of returned optical signals to interfere with each other and outputting them as the return optical signal to the light emitting element side And
An optical fiber loop that introduces the pair of optical signals branched at the optical connection portion in different rotation directions and feeds back to the optical connection portion;
A detection unit for detecting vibration of the optical fiber loop based on the electrical signal output by the light receiving element;
An optical fiber vibration sensor.
[2] The optical connection unit branches the introduction optical signal output from the light emitting element into a first optical signal by transmission and a second optical signal by coupling, and is fed back from the optical fiber loop. The first optical signal by and the second optical signal by transmission fed back from the optical fiber loop interfere with each other and output to the light emitting element side as the return optical signal.
The optical fiber vibration sensor according to [1].
[3] The detection unit detects vibration of the optical fiber loop based on a phase difference between the first and second optical signals obtained from the electrical signal output from the light receiving element.
The optical fiber vibration sensor according to [2].
[4] The optical fiber vibration sensor according to [2] or [3], further including a phase modulation unit that modulates phases of the first and second optical signals branched by the optical connection unit.
[5] An optical fiber coil that delays the first or second optical signal branched by the optical connection unit and causes a time difference for the first and second optical signals to reach the optical fiber loop, The optical fiber vibration sensor according to any one of [2] to [4], further provided.
[6] The light emitting element outputs the optical signal having polarization characteristics.
The optical fiber vibration sensor according to any one of [1] to [5].

  According to the present invention, it is possible to reduce the branch loss of an optical signal and to perform highly accurate vibration measurement using a reciprocal optical system.

FIG. 1 is a diagram illustrating a configuration example of an optical fiber vibration sensor according to an embodiment of the present invention. FIG. 2A is a schematic diagram illustrating transmission of an optical signal when the optical signal is branched, and FIG. 2B is a schematic diagram illustrating transmission of the optical signal when the optical signal is interfered. FIG. 3 is a block diagram illustrating an example of a circuit of the signal processing unit. FIG. 4 is a cross-sectional view of the sensor cable. 5A is a cross-sectional view of an elliptical jacket type PMF, and FIG. 5B is a cross-sectional view of an elliptical core type PMF. FIG. 6 is a diagram illustrating a state in which the optical fiber vibration sensor is installed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, in each figure, about the component which has the substantially same function, the same code | symbol is attached | subjected and the duplicate description is abbreviate | omitted.

[Summary of embodiment]
The optical fiber vibration sensor of this embodiment is a Sagnac interference type optical fiber vibration sensor that detects vibration of an optical fiber loop, and outputs an introduction optical signal and self-couples a return optical signal of the output optical signal. A light emitting element that outputs a detection optical signal amplified by the effect, a light receiving element that converts the detection optical signal output from the light emitting element into an electrical signal, and outputs the light, and the introduction light output from the light emitting element A signal is split into a pair of optical signals, and a pair of optical signals that have been fed back are interfered with each other and output to the light emitting element side as the return optical signal, and the optical connection unit branches An optical fiber loop that introduces the pair of optical signals in different rotational directions and feeds them back to the optical connection portion, and the optical fiber based on the electrical signal output from the light receiving element. And a detecting section for detecting a vibration of the loop.

[Embodiment]
FIG. 1 is a diagram illustrating a configuration example of an optical fiber vibration sensor according to an embodiment of the present invention. As shown in FIG. 1, the optical fiber vibration sensor 1 is a Sagnac interference type optical fiber vibration sensor including a vibration sensor main body 2 and an optical fiber loop 3 in which an optical fiber is formed in a loop shape.

(Vibration sensor body)
The vibration sensor main body 2 emits the optical signal S ₁ and receives the return optical signal S ₂ , and the light signal S ₁ output from the light emitting / receiving unit 21 as a pair of optical signals S _11. , S ₁₂ , an optical coupler 22 that branches the optical signals S ₁₁ and S ₁₂ branched by the optical coupler 22, and a phase modulator 24 that modulates the phases of the optical signals S ₁₁ and S _12. And a signal processing unit 25 that detects vibration of the optical fiber loop 3 based on the phase difference between the pair of optical signals S ₁₁ and S ₁₂ and controls the light emitting and receiving unit 21 and the phase modulator 24, and an optical fiber loop 3 and an optical connector 26 that connects the vibration sensor main body 2 and optical fibers 200a, 200b, and 200c that serve as paths of optical signals S ₁ , S ₁₁ , S ₁₂ , and a return optical signal S ₂ . The optical coupler 22 is an example of an optical connection unit. The optical signal S ₁ is an example of an introduction optical signal, the optical signal S ₁₁ is an example of a first optical signal, and the optical signal S ₁₂ is an example of a second optical signal. The phase modulator 24 is an example of a phase modulation unit, and the signal processing unit 25 has a function as a detection unit.

(Light emitting / receiving part)
The light emitting / receiving unit 21 outputs the optical signal S ₁ having polarization characteristics based on the current output from the signal processing unit 25 via the signal line 201 and transmits the return optical signal S ₂ of the optical signal S _1. Te and the light emitting element 211 for outputting an optical signal S _2a amplified by self-coupling effect on the rear side, provided on the back side of the light emitting element 211 converts the optical signal S _2a of the light-emitting element 211 outputs an electric signal, the signal It comprises a light receiving element 212 to output over line 201 to the signal processing unit 25, and condenses the light signals _{S 1} output from the light emitting element 211 to the optical fiber 200a and lens 213 for optical coupling. The optical signal _S2a is an example of a detection optical signal.

  The light emitting element 211 is a semiconductor laser that outputs an optical signal. For example, a CD-LD (Laser Diode for Compact Disc Player) that is a low-cost multimode semiconductor laser used in a compact disc player or the like is used. For example, a photodiode is used as the light receiving element 212.

The lens 213 is provided on the surface side of the light emitting element 211, optically couples the optical signal S ₁ with the optical fiber 200 a, and propagates the return optical signal S ₂ output from the optical coupler 22 in parallel to the light emitting element 211. The lens 213 can be made of, for example, an acrylic or epoxy resin, quartz glass, or the like.

The self-coupling effect of the light emitting element 211 is due to interference and amplification phenomenon occurring in the active layer of the semiconductor laser, and has high wavelength selectivity. Therefore, the light emitting element 211 amplifies only the return optical signal S ₂ having the same wavelength as the output optical signal S ₁ by the self-coupling effect and outputs the amplified signal to the light receiving element 212 on the back side. The light-emitting / receiving unit 21 including the light-emitting element 211 and the light-receiving element 212 having the self-coupling effect can be configured by only the semiconductor laser package and the lens 213. By using this semiconductor laser package, the optical components of the vibration sensor main body 2 can be omitted, and the assembly process of the vibration sensor main body 2 can be simplified. Further, since it becomes possible to selectively amplify the return optical signal S _2, it becomes possible to detect with high accuracy small optical signal.

(Optical fiber)
Optical fibers 200a, 200b, and 200c for connecting the light emitting / receiving unit 21, the optical coupler 22, the optical fiber coil 23, the phase modulator 24, and the optical connector 26 are shown in FIGS. 5A and 5B described later. It is preferable to use a polarization-maintaining fiber.

(Optical coupler)
FIG. 2A is a schematic diagram illustrating transmission of an optical signal when the optical signal is branched, and FIG. 2B is a schematic diagram illustrating transmission of the optical signal when the optical signal is interfered. The optical coupler 22 branches the optical signal S ₁ output from the light emitting element 211 via the optical fiber 200 a into a pair of optical signals S ₁₁ and S ₁₂ , and connects the pair of optical fibers 200 b and 200 c and the optical connector 26. Then, a return optical signal S ₂ obtained by interfering with the pair of optical signals S ₁₁ and S ₁₂ fed back from the optical fiber loop 3 is output to the light emitting element 211 side.

That is, the optical coupler 22, as shown in FIG. 2 (a), the optical signal _{S 11} optical signals _{S 1} output from the light emitting element 211 by transmission branches the optical signal _{S 12} by bonding. As shown in FIG. 2B, the optical coupler 22 causes the optical signal S ₁₁ resulting from the coupling fed back from the optical fiber loop 3 to interfere with the optical signal S ₁₂ resulting from the transmission, and sends the return optical signal S ₂ to the light emitting element 211 side. Output to.

The pair of optical signals S ₁₁ and S ₁₂ branched and interfered by the optical coupler 22 is transmitted to the light emitting element 211 side as a return optical signal S ₂ after passing and coupling once. Therefore, the paths through which the optical signals S ₁₁ and S ₁₂ are output are reciprocal.

(Optical fiber coil)
As shown in FIG. 1, one end of the optical fiber coil 23 is connected to the optical coupler 22 by an optical fiber 200b, and the other end is connected to the optical fiber loop 3 through the optical fiber 200b and the optical connector 26. The optical fiber coil 23 includes an optical fiber having substantially the same length as the entire length of the optical fiber loop 3, and makes the sensitivity for detecting vibration of the optical fiber loop 3 constant in the length direction of the optical fiber loop 3.

That is, the optical fiber coil 23 delays the optical signal S ₁₁ or the optical signal S ₁₂ branched by the optical coupler 22, thereby causing a time difference for the optical signals S ₁₁ and S ₁₂ to reach the optical fiber loop 3. Sensitivity for detecting vibration in the length direction of the optical fiber loop 3 is made constant.

(Phase modulator)
The phase modulator 24 includes a cylindrical piezoceramic and an optical fiber wound around the piezoceramic. One end of the phase modulator 24 is connected to the optical coupler 22 through the optical fiber 200 c, the other end is connected to the optical fiber loop 3 through the optical fiber 200 c and the optical connector 26, and the signal processing unit 25 is connected through the signal line 201. Connected to. For example, PZT (lead zirconate titanate) is used as the piezoceramic.

For example, when a sine wave voltage having a phase modulation frequency of 22 kHz, which is a resonance frequency of the piezo ceramic, is supplied from the signal processing unit 25, the phase modulator 24 vibrates the piezo ceramic due to the sine wave voltage. The phase of the optical signals S ₁₁ and S ₁₂ is modulated by expanding and contracting the wound optical fiber.

By modulating the phases of the optical signals S ₁₁ and S _{12 by} the phase modulator 24, a time difference for the modulated optical signals S ₁₁ and S ₁₂ to reach the optical coupler 22 is generated, so that the optical signals S ₁₁ and S ₁₂ have a time difference. A phase difference is induced, and a return signal S ₂ based on this phase difference is received by the light receiving element 212.

(Signal processing part)
FIG. 3 is a block diagram illustrating an example of a circuit of the signal processing unit. The signal processing unit 25 removes the DC component of the electrical signal output from the light receiving element 212 and passes the AC component, and the preamplifier 252 that amplifies the AC component of the electrical signal that has passed through the transimpedance circuit 251. A control circuit 254 that performs output control of the light emitting element 211 based on the electrical signal output from the preamplifier 252; a drive circuit 255 that supplies current to the light emitting element 211 based on output control performed by the control circuit 254; A lock-in amplifier 253 for detecting a plurality of predetermined frequencies of the electric signal amplified in 252; an A / D conversion circuit 257 for converting an analog signal output from the lock-in amplifier 253 into a digital signal; Phase modulation frequency component of the optical signal S _2a based on the digital signal obtained And a CPU (Central Processing Unit) 256 for detecting the vibration of the optical fiber loop 3 by calculating the output ratio of its harmonic components.

One end of the transimpedance circuit 251 is electrically connected to the light receiving element 212 via the signal line 201, and the other end is electrically connected to the preamplifier 252. The transimpedance circuit 251 is provided with a capacitor C ₁ and resistor R _1, it constitutes a RC circuit, one end of the resistor R ₁ is connected to a reference potential.

  The transimpedance circuit 251 prevents the output of the preamplifier 252 from being saturated by outputting an alternating current component from which the direct current component included in the electrical signal output from the light receiving element 212 is removed to the preamplifier 252.

  The preamplifier 252 has one end electrically connected to the transimpedance circuit 251 and the other end electrically connected to the lock-in amplifier 253 and the control circuit 254. The preamplifier 252 outputs the amplified electrical signal to the lock-in amplifier 253 and the control circuit 254.

  The control circuit 254 has one end electrically connected to the preamplifier 252 and the other end electrically connected to the drive circuit 255. The control circuit 254 integrates all the output of the phase modulation frequency component and its harmonic component output from the preamplifier 252 and changes the supply current of the light emitting element 211 so that the integrated frequency component value (amplitude value) becomes constant. Control.

  For example, the control circuit 254 acquires the reference value of the frequency component integrated in advance in a state where the sensor cable 300 is attached to a vibration measurement target such as a fence, so that the value of the integrated frequency component becomes constant. The supply current to 211 is controlled. That is, all the outputs of the phase modulation frequency component and its harmonic component are integrated over a certain period t, and the value of the integrated frequency component is stored in a memory (not shown) as a reference value. Then, the control circuit 254 controls the supply current to the light emitting element 211 so that the amplitude value of the frequency component obtained by integrating the output of the phase modulation frequency component and its harmonic component is equal to the previously stored reference value. . The reason why the reference value is stored in the memory with the sensor cable 300 attached is that the reference value changes depending on the installation status of the optical fiber loop 3.

  One end of the drive circuit 255 is electrically connected to the control circuit 254, and the other end is electrically connected to the light emitting element 211 via the signal line 201. The drive circuit 255 drives the light emitting element 211 based on the output control of the control circuit 254.

  The lock-in amplifier 253 has one end electrically connected to the preamplifier 252 and the other end electrically connected to the CPU 256 via the A / D converter 257. The lock-in amplifier 253 detects a plurality of predetermined frequency components among the frequency components included in the electrical signal amplified by the preamplifier 252. The lock-in amplifier 252 smoothes and amplifies signals corresponding to the amplitudes of the detected plurality of frequency components, and outputs the signals to the CPU 256 via the A / D converter 257.

The CPU 256 inputs a signal from the lock-in amplifier 252 via the A / D converter 257. The signal includes a phase modulation frequency component and its harmonic components (for example, second-order and fourth-order components) as a plurality of frequency components. The CPU 256 obtains the ratio between the amplitude value of the phase modulation frequency component and the amplitude value of the harmonic component (for example, the secondary component), and calculates the phase difference between the optical signals S ₁₁ and S ₁₂ from the ratio of the amplitude values. The CPU 256 is connected to the phase modulator 24 via a D / A converter and a signal line 201 (not shown), and outputs an electrical signal to the phase modulator 24 to vibrate the piezoelectric ceramic of the phase modulator 24. Controls the phase modulation of the optical signals S ₁₁ and S ₁₂ .

(Optical fiber loop)
FIG. 4 is a cross-sectional view of the sensor cable. FIG. 5A is a cross-sectional view of an elliptical jacket type PMF, and FIG. 5A is a cross-sectional view of an elliptical core type PMF.

As shown in FIG. 1, the optical fiber loop 3 includes a sensor cable 300 into which a pair of optical signals S ₁₁ and S ₁₂ is introduced, and a pair of optical signals S ₁₁ and S ₁₂ branched by an optical coupler 22. Are introduced via the optical connector 26 in different rotational directions. The optical fiber loop 3 feeds back the introduced optical signals S ₁₁ and S ₁₂ to the optical coupler 22.

  As shown in FIG. 4, the sensor cable 300 includes two optical fibers 301, a reinforcing fiber 302 that reinforces the optical fiber 301, a reinforcing member 303 that prevents the optical fiber 301 from being bent and stretched, an optical fiber 301, And a covering member 304 that covers the reinforcing fiber 302 and the reinforcing member 303.

  The optical fiber 301 used for the sensor cable 300 is a polarization maintaining fiber (PMF) in order to prevent the vibration detection from becoming unstable due to the rotation of the polarization of the optical signal. As the polarization-preserving fiber, an elliptic jacket type PMF shown in FIG. 5A, an elliptic core type PMF shown in FIG. 5B, or the like is used.

  As shown in FIG. 5A, the elliptical jacket type PMF 301a includes a core 310a, a clad 311a, an elliptical jacket 312 and a support 313. The elliptical jacket 312 applies stress to the core 310a so as to obtain a desired birefringence. The elliptic jacket type PMF 301a is used for the sensor cable 300 including the long-distance optical fiber 301 because it has low transmission loss and high polarization maintaining characteristics.

  As shown in FIG. 5B, the elliptical core type PMF 301b includes a core 310b and a clad 311b having an elliptical cross-sectional shape. The elliptical core type PMF 301b is low in cost but has difficulty in long-distance characteristics, and thus is used for the sensor cable 300 having a relatively short distance.

(Installation example of optical fiber vibration sensor)
FIG. 6 is a diagram illustrating an installation example of the optical fiber vibration sensor 1. In the optical fiber vibration sensor 1, the housing 20 housing the vibration sensor main body 2 is attached to the column part 41 of the fence 4, and the sensor cable 300 is fixed to the wire mesh 42 of the fence 4 and installed on the fence 4. The sensor cable 300 forming the optical fiber loop 3 is connected to the optical connector 26 of the vibration sensor main body 2 housed in the housing 20 at both ends.

(Operation of optical fiber vibration sensor)
Hereinafter, an example of the operation of the optical fiber vibration sensor 1 will be described.

The light emitting element 211 outputs the optical signal S ₁ based on the electrical signal output from the signal processing unit 25. The optical signal S ₁ is transmitted to the optical coupler 22 and branched by the optical coupler 22 into an optical signal S ₁₁ by transmission and an optical signal S ₁₂ by combination.

One of the optical signal _{S 11} of the optical signal _{S 11, S 12} of a pair split by the optical coupler 22 via the optical fiber coil 23 enters the optical fiber loop 3, the other optical signal _{S 12} is The phase of the optical signal S ₁₂ is modulated by the phase modulator 24 and is incident on the optical fiber loop 3. The optical signals S ₁₁ and S ₁₂ are transmitted through the optical fiber loop 3 in different rotation directions.

The pair of optical signals S ₁₁ and S ₁₂ introduced into the optical fiber loop 3 circulates around the optical fiber loop 3 and returns to the optical coupler 22 via the optical fiber coil 23 or the phase modulator 24. The optical coupler 22 outputs the return light signal S2 obtained by interference between optical signals S ₁₂ by the feedback was transmitted optical signal S ₁₁ by the feedback binding to the light emitting element 211 side. When the optical fiber loop 3 vibrates, a phase difference occurs between the optical signals S ₁₁ and S ₁₂ due to expansion and contraction of the optical fiber 301.

Emitting element 211 returning light signal S ₂ output in is transmitted through the light emitting element 211, is output to the light receiving element 212 provided on the back side of the light emitting element 211 as an amplified optical signal S _2a by self-coupling effect .

The optical signal S _2a output to the light receiving element 212 is converted into an electric signal by the light receiving element 212 and output to the signal processing unit 25.

  When an electrical signal is output from the light receiving element 212 to the signal processing unit 25, the DC component of the electrical signal is first removed from the electrical signal by the transimpedance circuit 251. The electric signal from which the DC component is removed is amplified by the preamplifier 252 and output to the control circuit 254 and the lock-in amplifier 253.

  One electrical signal output from the preamplifier 252 is detected and amplified by a plurality of frequency components determined in advance by the lock-in amplifier 253, and is output to the CPU 256 as a digital signal via the A / D conversion circuit 257. The

The CPU 256 obtains the ratio of the amplitude value of the phase modulation frequency component and the harmonic component of the phase modulation frequency component based on the digital signal output from the lock-in amplifier 253 via the A / D converter 257, and The phase of the optical signals S ₁₁ and S ₁₂ is calculated from the ratio of the amplitude values to detect the vibration of the optical fiber loop 3.

  The other electric signal output from the preamplifier 252 is integrated by the control circuit 254 with the voltage value of the AC component of the electric signal. The control circuit 254 integrates all the outputs of the phase modulation frequency component and its harmonic component, and controls the supply current of the light emitting element 211 so that the amplitude of the integrated frequency component becomes constant.

(Effect of embodiment)
According to the present embodiment, the following effects can be obtained.
(A) By receiving the optical signal S _2a obtained by amplifying the return optical signal S ₂ of the optical signal S ₁ output from the light emitting element 211 by the light receiving element 212 provided on the back side of the light emitting element 211, the optical coupler 22 is set to 1 Even in the single configuration, the paths of the optical signals S ₁₁ and S ₁₂ can be reciprocal optical systems, so that the phase difference of the optical signal due to transmission and coupling is reduced, and highly accurate vibration measurement is possible.
That is, the optical signal passing through the optical coupler has a phase difference of 90 degrees between the optical signal due to transmission and the optical signal due to coupling, but the optical signals S ₁₁ and S ₁₂ are transmitted as in the present embodiment. By using a reciprocal optical system in which the coupling is transmitted once each, the influence of the phase difference due to transmission and coupling can be reduced.
(A) Since the branching loss of the return optical signal S ₂ can be reduced by using one optical coupler 22, the output of the return optical signal S ₂ is compared with the configuration including two optical couplers 22. Can be reduced to about half. Furthermore, the number of parts of the optical fiber vibration sensor 1 can be reduced and the process of assembling the vibration sensor main body 2 can be simplified.
(C) The signal processing unit 25 detects the vibration of the optical fiber loop 3 based on the phase difference between the optical signals S ₁₁ and S ₁₂ , thereby affecting the influence of the amplification factor of the preamplifier 252 and the modulation efficiency of the phase modulator 24. Since the number can be reduced, vibration detection of the optical fiber loop 3 can be performed with high accuracy.
(D) By providing the optical fiber coil 23 at one end of the optical fiber loop 3, the sensitivity of detecting the vibration of the optical fiber loop 3 can be adjusted, so that the accurate vibration detection of the optical fiber loop 3 becomes possible. .
By modulating the phase of the optical signal _{S 11, S 12} provided (e) a phase modulator 24, it is possible to induce a phase difference between the optical signals _{S 11, S 12,} thereby the optical fiber loop 3 Sensitivity for detecting vibration with respect to a small phase difference due to vibration can be increased.
(F) Since the light emitting element 211 outputs the optical signal S ₁ having polarization characteristics, a configuration that does not require a polarizer used in a conventional optical fiber vibration sensor can be adopted. The score can be reduced.
(G) The control circuit 254 integrates all the output of the phase modulation frequency component and its harmonic component included in the electrical signal output from the light receiving element 212, and the control circuit 254 controls the output of the light emitting element 211. it is possible to maintain the output level of the return light signal S ₂ incident on the light receiving element 212 at a constant, it is possible to maintain the vibration detection sensitivity of the optical fiber loop 3.

[Modification]
The embodiment of the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the gist of the present invention. For example, in the above embodiment, the CD-LD is used as the light emitting element 211. However, a semiconductor light emitting element such as an SLD (Super Luminescent Diode) may be used.

  When a light emitting element that outputs an optical signal having no polarization characteristic is used, a polarizer may be inserted in the optical signal path.

  Moreover, it is good also as a structure which can install a pair of vibration sensor main-body part 2 and the optical fiber loop 3 in the fence 4 grade | etc., And can identify a vibration location by the sensitivity difference of vibration detection. Moreover, it is good also as a structure which installs a warning device in the fence 4 grade | etc.,.

  Moreover, it is also possible to remove some of the constituent elements of the above-described embodiment within a range not changing the gist of the present invention.

  The present invention can be applied as, for example, a vibration sensor for detecting an intruder, a disaster prevention sensor for detecting earthquakes, and falling rocks.

DESCRIPTION OF SYMBOLS 1 Optical fiber vibration sensor 2 Vibration sensor main-body part 3 Optical fiber loop 4 Fence 20 Housing 21 Light emission light reception part 22 Optical coupler 23 Optical fiber coil 24 Phase modulator 25 Signal processing part 26 Optical connector 41 Pillar part 42 Wire mesh 200a, 200b, 200c Optical fiber 201 Signal line 211 Light-emitting element 212 Light-receiving element 213 Lens 251 Transimpedance circuit 252 Preamplifier 253 Lock-in amplifier 254 Control circuit 255 Drive circuit 256 CPU
300 Sensor cable 301 Optical fiber 302 Reinforcing fiber 303 Reinforcing member 304 Covering member 310a, 310b Core 311a, 311a Cladding 312 Elliptical jacket 313 Support 301a Elliptic jacket type PMF
301b Elliptical core type PMF
C ₁ capacitor R ₁ resistor S ₁ , S ₁₁ , S ₁₂ , S _2a optical signal S ₂ return optical signal

Claims (6)

A light-emitting element that outputs an introduction signal and outputs a detection optical signal that is amplified by a self-coupling effect by transmitting a return optical signal of the introduced introduction optical signal;
A light receiving element that receives the detection optical signal output from the light emitting element, converts the detection signal into an electrical signal, and outputs the electrical signal;
An optical connection for branching the introduction optical signal output from the light emitting element into a pair of optical signals and causing the pair of returned optical signals to interfere with each other and outputting them as the return optical signal to the light emitting element side And
An optical fiber loop that introduces the pair of optical signals branched at the optical connection portion in different rotation directions and feeds back to the optical connection portion;
A detection unit for detecting vibration of the optical fiber loop based on the electrical signal output by the light receiving element;
An optical fiber vibration sensor. The optical connecting portion branches the introduction optical signal output from the light emitting element into a first optical signal by transmission and a second optical signal by coupling, and the first by the coupling fed back from the optical fiber loop. 1 optical signal and the second optical signal due to transmission fed back from the optical fiber loop are interfered with each other and output to the light emitting element side as the return optical signal.
The optical fiber vibration sensor according to claim 1. The detection unit detects vibration of the optical fiber loop based on a phase difference between the first and second optical signals obtained from the electrical signal output from the light receiving element;
The optical fiber vibration sensor according to claim 2. The optical fiber vibration sensor according to claim 2, further comprising a phase modulation unit that modulates a phase of the first and second optical signals branched by the optical connection unit. An optical fiber coil that delays the first or second optical signal branched by the optical connecting unit and causes a time difference for the first and second optical signals to reach the optical fiber loop;
The optical fiber vibration sensor according to any one of claims 2 to 4, further comprising: The light emitting element outputs the introduction optical signal having polarization characteristics.
The optical fiber vibration sensor according to any one of claims 1 to 5.

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